Sulphur mustards (SM), is sadly famous after its extensive use on the battle fields of World War I and more recently in Iraq. This chemical is rather simple to synthesize and, in addition to its military applications, could thus be used in terrorism acts. Consequently, the deleterious properties of SM have regained attention. SM targets three mains organs, namely lungs, eyes and skin. In a recent collaborative work with the Army Institute for Biomedical Research (IRBA, La Tronche) we investigated the effects of SM in skin, and in particular the genotoxicity of such exposure. Indeed, it is well documented that induction DNA damage is a major pathway in the acute effects of SM and that this compound is also carcinogenic on the long term. Such research efforts are motivated by the need to better understand the pathological process in order to develop new treatments. A hairless mice model, SKH1, was used.

Evolution of the level of adducts in skin of SKH-1 mice exposed to SM.

We developed an HPLC-tandem mass spectrometry assay for the N7 adducts to Guanine and Adenine as well as for the biadduct between SM and two guanine moiety. A specific hydrolysis procedure was developed because the targeted adducts are not stable and undergo hydrolytic depurination. Using this technique, we were able to detect adducts at high and low concentration of applied SM. Interestingly, SM-adducts were detected in significant amounts in the skin adjacent to the exposed zone only at the highest concentration. This result show that the barrier function of the skin remains intact over a wide range of dose. We then quantified the level of DNA adducts over a large period of time are were still able to detect them three weeks after exposure in spite of a significant decrease during the first days.

Level of SM in internal organs of mice exposed to SM

SM is known to diffuse through skin and reach the blood flow from where it diffuses into internal organs. For this reason, we extracted DNA from brain, lungs, liver, kidney and spleen and quantified DNA adducts. Those where present in significant amounts except in the liver where they were detected only at the largest dose. Interestingly, brain was the most concerned organ in terms of DNA damage. Like in skin, adducts where detected over a long period of time. They were also detected in much larger amount at the largest dose, suggesting again that, under these conditions, the barrier function of skin was lost. Last, we quantified the DNA repair activities in the internal organs and observed a trend to a decrease upon exposure to SM.

Altogether tis work shows that SM is a potent genotoxic agent which induces large amounts of DNA damage upon cutaneous contact, both in skin and in internal organs. The impact on DNA repair would likely worsen the toxic consequence of the exposure. The persistence of the adducts, suggesting a reservoir effect, make them possible biomarkers of exposure for instance in blood cells.

This work was supported by the ANR project “ToxYp” and by the Direction Générale de l’armement.